Fun fact: Is leg shaking really bad?

"Men shake their legs when they are poor, women shake their legs when they are cheap", this popular saying associates the body movement of "shaking legs" with social status, and is often used by elders to admonish children and persuade them to change the uncivilized habit of "shaking legs". So, why do people at certain moments cannot help but step on the "empty pedal"?

I couldn't help shaking my legs.

Maybe it's the emotions messing up.

In fact, leg shaking is a typical body language. When it occurs, it often means that the person shaking his legs is in a state of tension, boredom or high excitement. For example, studies have shown that during exams, anxious low-scoring candidates can't help shaking their legs, while confident high-scoring candidates don't move their legs too frequently.

To explain why people shake their legs when facing stress, we need to start with a concept proposed by physiologist Walter B. Cannon in 1929: When animals perceive stress or threats to survival, they release adrenaline under the action of the sympathetic nerves, which causes physiological reactions such as faster heartbeat, higher pulse, and more blood flowing to the limbs. This physiological reaction helps animals respond quickly when danger comes, helping them survive better. Cannon named this concept the "fight-flight response", or the "fight or flight" response. Because this is a "life-saving" mechanism in which the body responds to survival before the brain, it has helped ancient human ancestors escape from natural enemies or compete for survival resources, so it has been preserved in the long evolution and continues to accompany us in various forms such as "accelerated heartbeat during quarrels", "blushing when confessing love", and "wanting to have diarrhea when nervous".

What is the connection between the "fight or flight" response and leg shaking? In a health consultation article in the British Metro newspaper, psychologist Dawn Templeton and clinical psychologist Catherine Huckle expressed their views: under stress and anxiety, adrenaline and cortisol accumulate, and the body accumulates energy under the action of the "fight or flight" response to prepare for stress. But when we don't use up this energy through self-defense or escape, the excess energy will remain in our body, and leg shaking is a way to release this energy. In other words, leg shaking is like a fake move used by the brain to deceive itself. Since the buttocks still need to sit honestly on the chair, it is difficult to vent the excess energy by shaking the legs.

Image source: pixabay

Legs may also shake when you are bored. Studies have shown that when the mind starts to wander, the body will also "wander" and make small movements. This may be because boredom can bring anxiety and frustration to people, causing stress hormones to accumulate, and body movements such as shaking legs, playing with hair, and spinning pens can help release stress. However, it should be noted that long-term repetition of these behaviors will form fixed habits. If you forcefully correct them at this time, it will increase the feeling of irritability. For example, if a person usually has the habit of shaking his legs, and deliberately reminds himself not to shake his legs during an important interview, he may become restless and even ruin the entire interview.

In addition to shaking legs when in a state of anxiety, people will also shake their legs unconsciously to the rhythm of the melody when listening to their favorite music. This is because music is a special sensory stimulation that activates body movements unconsciously. In addition, researchers at the University of Oslo in Norway found that shaking legs regularly to the rhythm of music can help the brain better understand music.

Shaking your legs is very comfortable.

May improve the harm of prolonged sitting

Leg shaking is not only a very natural behavior, but also through leg shaking, the brain will secrete dopamine and other hormones related to pleasant emotions, producing a "refreshing" feeling.

But some people may worry about whether leg shaking will cause health hazards. In fact, properly exercising muscles through actions such as leg shaking may alleviate the harm caused by sitting for a long time.

Researchers at the University of Missouri recruited 11 volunteers and used ultrasound and blood pressure cuffs to measure the blood flow in the main arteries of each person's legs under normal circumstances. The volunteers were then asked to sit quietly at a table for three hours, keeping one leg absolutely still and the other leg shaking from time to time (shaking for 1 minute, and staying still for 4 minutes). The results showed that compared with the initial value, the blood flow of the stationary leg was significantly reduced, while the blood flow of the shaking leg increased.

Another study from the University of Houston found that if sedentary people effectively exercise the soleus muscle in their calves, they can also improve muscle metabolism and even improve blood sugar and blood lipids. This method of training the soleus muscle is very similar to shaking legs, that is, keep sitting, relax your feet first, then lift your heels, keep your toes on the ground, and when the heels are raised to the limit and the soleus muscles have a noticeable stretch, the heels fall back to the ground.

However, it should be noted that the sample size of these two studies is small and can only provide limited reference value. And if you want to completely avoid the health damage caused by sitting for a long time, the best way is to stand up and move around.

In general, although the small action of shaking legs is beneficial to the body and mind in certain specific situations, you need to pay attention to the posture and occasion. After all, frequent shaking legs is a way of expressing irritability with body language, which is impolite behavior. Therefore, instead of developing the habit of shaking legs, it is better to learn scientific relaxation methods instead.

Pathological leg shaking

Need to be treated with caution

Although physiological leg shaking is basically harmless except for being culturally impolite, pathological leg shaking is related to certain diseases and needs to be carefully identified so that it can be treated as soon as possible.

The most typical clinical disease of leg tremors is restless legs syndrome, which is a sensory motor disorder. Simply put, patients will feel indescribable paresthesia and discomfort in both lower limbs in a quiet state, and need to shake or tap a few times to relieve the pain. The biggest feature of this disease is that it will get worse when resting at night.

Leg shaking is also a common self-stimulatory behavior in autistic patients. Autistic patients often feel anxious and overwhelmed by external noise or lights. Self-stimulatory behaviors such as leg shaking, rubbing hands, and biting fingers can help them distract their attention, calm their emotions, and restore their sense of control over their bodies. Similarly, patients with ADHD and anxiety disorders often shake their legs to cope with anxiety and concentrate their attention.

References

[1]https://www.goodtherapy.org/blog/foot-tapping-hand-flapping-why-do-people-stim-0104194

[2]https://williamsburgtherapygroup.com/blog/is-foot-tapping-a-sign-of-anxiety#:~:text=Because%20anxiety%20disorders%20manifest%20as,behaviors%20can%20often%20cause%20problems.

[3]https://metro.co.uk/2019/04/20/anxious-leg-bounce-happens-deal-9277508/

[4] Gregersen, TS (2005). Nonverbal cues: Clues to the detection of foreign language anxiety. Foreign language annals, 38 (3), 388-400.

[5]Toiviainen,P.,Luck,G.,&Thompson,MR(2010).Embodiedmeter:hierarchicaleigenmodesinmusic-inducedmovement.MusicPerception,28(1),59-70.

[6] Godøy, RI, Song, M., Nymoen, K., Haugen, MR, & Jensenius, AR (2016). Exploring Sound-Motion Similarity in Musical Experience. Journal of New Music Research, 45 (3), 210–222.

[7]Morishima, T., Restaino, RM, Walsh, LK, Kanaley, JA, Fadel, PJ, & Padilla, J. (2016). Prolongedsitting-induced legendothelialdysfunctionispreventedbyfidgeting. American Journal of Physiology-HeartandCirculatoryPhysiology, 311(1), H177-H182.

[8]Hamilton,MT,Hamilton,DG,&Zderic,TW(2022).Apotentphysiologicalmethodtomagnifyandsustainsoleusoxidativemetabolismimprovesglucoseandlipidregulation.Iscience,25(9).

[9]Kapp,SK,Steward,R.,Crane,L.,Elliott,D.,Elphick,C.,Pellicano,E.,&Russell,G.(2019).'Peopleshouldbeallowedtodowhattheylike':Autisticadults'viewsandexperiencesofstimming.Autism, 23(7),1782-1792.

[10] CarriereJSA,SeliP,SmilekD.Wanderinginbothmindandbody:individualdifferencesinmindwanderingandinattentionpredictfidgeting.CanJExpPsychol.2013Mar;67(1):19-31.doi:10.1037/a0031438.PMID:23458548.

[11]McCarty, R.(2016).Thefight-or-flightresponse:Acornerstoneofstressresearch.InStress:Concepts,cognition,emotion,andbehavior(pp.33-37).AcademicPress.

This article is a work of Science Popularization China-Starry Sky Project

Produced by: Science Popularization Department of China Association for Science and Technology

Producer｜China Science and Technology Press Co., Ltd., Beijing Zhongke Xinghe Culture Media Co., Ltd.

Author: Hardy, PhD in Neurobiology, Zhejiang University

Reviewer: Mao Lihua, Associate Professor, School of Psychology and Cognitive Science, Peking University